WASHINGTON, June 13 (Reuters) - President Barack Obama said on Friday he needs several days to determine how the United States will help Iraq deal with a militant insurgency, but he ruled out sending U.S. troops back into combat and said any intervention would be contingent on Iraqi leaders becoming more involved.

The Pentagon is preparing a range of options for Obama, including air strikes. The actions are aimed at helping Iraq counter militants of the Islamic State in Iraq and the Levant, or ISIL, a group Obama described as "vicious" and a "terrorist organization" that could eventually pose a threat to Americans.

Obama said Iraqi leaders needed to set aside sectarian differences to deal with the threat, and said the United States would engage in "intensive diplomacy" in the region to try to prevent the situation from worsening.

"The United States is not simply going to involve itself in a military action in the absence of a political plan by the Iraqis that gives us some assurance that they are prepared to work together," Obama told reporters at the White House.

Obama said he would consult with the U.S. Congress in coming days. His fellow Democrats are reluctant to allow any U.S. engagement in Iraq after the lengthy war, which began with the 2003 U.S.-led invasion to topple President Saddam Hussein.

"It is important to remember that military force alone cannot bring peace," said Adam Smith, the top Democrat on the House of Representatives Armed Services Committee.

Republicans have been critical of the president for what they say has been dithering on Iraq.

"We shouldn't have boots on the ground, but we need to be hitting these columns of terrorists marching on Baghdad with drones now," said California Republican Ed Royce, the chairman of the House Foreign Affairs Committee.

Senators John McCain and Lindsey Graham, members of the Armed Services Committee, also called for air strikes. "This is a moment to deal ISIS a crippling blow, when they are over-stretched and least prepared for it," they said in a statement.

U.S. SURVEILLANCE IN IRAQ

The United States stepped up its intelligence, surveillance and reconnaissance support this week at Baghdad's request, said Pentagon spokesman Rear Admiral John Kirby. Some surveillance drones have been collecting data on rebel movements.

A spokesman for Lockheed Martin, which makes Hellfire missiles being sold to Iraq, said it would work with the U.S. government to accelerate those deliveries, if asked.

"We were surprised and disappointed by the poor performance of some Iraqi security force units (that are) up in the north. I'd be less than honest if I said that that performance instilled a lot of confidence. It didn't," he said.

US counterterrorism official, speaking on condition of anonymity, said ISIL appeared well positioned to keep the territory it has captured if it maintains the support Sunnis in the areas it has occupied and absent a major counteroffensive.

But he added: "The group faces the real prospect of overstretch if it tries to press deep into Baghdad and beyond."

Obama said he was concerned that ISIL could try to overrun Shi'ite sacred sites, creating sectarian conflicts "that could be very hard to stamp out." The rebels are Sunni Muslims and the Baghdad government of Prime Minister Nuri al-Maliki is dominated by Shi'ites.

"This is a regional problem, and it is going to be a long-term problem. And what we're going to have to do is combine selective actions by our military to make sure that we're going after terrorists who could harm our personnel overseas or eventually hit the homeland," Obama said.

Obama said he wanted to review intelligence on the situation in Iraq so that any U.S. actions are "targeted, they are precise, and they are going to have an effect."

He noted that the U.S. has already "poured a lot of money into these Iraqi security forces."

Obama spoke with Canadian Prime Minister Stephen Harper about the crisis on Friday and was expected to talk to other foreign leaders about the situation over the weekend, White House spokesman Josh Earnest told reporters traveling with Obama on Air Force One on a previously scheduled trip to North Dakota. Obama was scheduled to spend the weekend in California.

Earnest said the Obama administration had not at this stage discussed potential interventions with Iran, Iraq's neighbor to the east and a backer of Maliki.

The United States and Iran, which have feuded since the 1979 Islamic revolution, would appear to have a joint interest in defeating the Sunni Muslim insurgents who have seized large swaths of northwestern Iraq. A senior Iranian official told Reuters that Iran might be willing to cooperate with Washington.

Obama said the insurgency so far had not caused major disruptions to oil supplies from Iraq, but that if insurgents took control of refineries, other oil producers in the Middle East would need to help "pick up the slack."

"That will be part of the consultations that will be taking place during the course of this week," Obama said. (Additional reporting by Jeff Mason, Susan Heavey, Eric Beech, Patricia Zengerle, Warren Strobel, Phil Stewart, Missy Ryan, Andrea Shalal; Editing by David Storey and Grant McCool)